Telephone system



Jan. 16, 1934. B. WALLACE 1,943,402

' TELEPHONE SYSTEM Filed June 16, 1932 2'SheetsSheet l I H 757E775? BEJTHZ/Z/a/[ac'E' 2 Sheets-Sheet 2 w mm a am. R

B. A. WALLACE TELEPHONE SYSTEM Filed June16, 1932 Jan. 16, 1934.

W w n H ur'ne BET'THl/Z/H/[HE'E JZL I Patented Jan. 16, 1934 STATESPATENT FFi 1'1".

TELEPHONE SYSTEM Application June 16,1932. Serial No. 617,537

17 Claims.

My invention relates to telephone systems and has to do moreparticularly with systems for interconnecting telephone linesterminating at the same or different exchanges and has for its object anovel and improved circuit arrangement.

The circuit of my invention is equally eflicient in interconnecting twosubscribers whose lines terminate at the same exchange or at diiierentexchanges associated with eachother by a 1g straightforward trunk.circuit as is well known in the art. Means are provided in the circuitwhich function upon the replacement of the subscribers receivers upontheir switchhooks to instantaneously disconnect the respective lines isfrom the cord. circuit to permit an immediate re call evidenced. by theillumination of the line lamp associated with the line of the callingsubscriber.

Another feature of my invention is the provision of means which placethe control of a local 2; to trunk connection under the supervision orthe local calling subscriber so that the trunk line is instantaneouslyreleased and ready for use in setting up another connection as soon asthe local calling subscriber hangs up provided the called subscriber hasnot answered or has previously replaced his receiver.

A further feature is theprovision of means which function when thecalling subscriber recalls on a local to trunk connection to switch frominstantaneous disconnect with line lamp recall to a flashing recallappearing only before the original operator so that she may properlytime and supervise the connection or attend the desires of the recallingsubscriber.

Another feature of my invention is the provision of a listening key inassociation with the keyless listening and secret service means operableon a local to local connection. The listening key permits the operatorto cut in only on local to 40 trunk connections for supervision purposesor to answer a recall on such a connection.

Further features of my circuit are selective party line machine ringingon local to local connections; dark keyshelf and double lamp discon- 5nect supervision; non-ringing on trunk connections and an automatic pegcount meter for answered calls.

Other features will become apparent upon a. further perusal of thespecification and together I with the features above enumerated, will beexplained fully hereinafter, reference being had to the accompanyingdrawings comprising Fig. 1 and Fig. 2 inclusive. When Fig. 2 is placedto the right of Fig. 1 they illustrate a complete circuit arrangementfor extending a connection from a subscriber at one exchange to asubscriber at a. distant exchange.

Referring now particularly to Fig. l, I illustrate at the left of thedrawing a calling common battery substation A terminating at a localexchange E in a line circuit L. The line circuit L comprises a linerelay LR, a cut off relay CO and multiple answering jacks J associatedwith multiple line lamps S. The jacks J and lamps S appear before aplurality of operators and a call initiated at the substation A willappear before a plurality of operators at different positions of theswitchboard as is well understood.

The link or cordcircuit C is but one of a plurality of similar cordcircuits furnished each of the operators and may be used to interconnecta pair of lines local to the exchange E or one of such lines with adistant exchange. This circuit C comprises an answering plug AP and acalling plug CP connected by the heavily marked or talking conductorshaving condensers CD and CD interposed therein. The answering end of thelink C consists of an answering sleeve relay ASL which is energized whenthe answering plug AP is inserted into a jack J of the calling line toconnect the operators set C) to the cord conductors. An answeringsupervisory relay ASR controlled by the switchhook of the calling linein turn controls an answering supervisory lamp AS provided for the usualsupervisory purposes. The 35 calling end of the link circuit C comprisescalling sleeve relays CSL and CSL; the said sleeve relay CSL operatingwhen connection is made with either a local line or with a trunk leadingto a distant exchange. The sleeve relay CSL' is a marginal relay andenergizes when connection is made with a trunk line but does notenergize when the cord C is connected to a local line.

An operators disconnect relay ODR is provided and energizes upon theoperation of the calling sleeve relay CSL to disconnect the operatorsset 0 from the cord conductors. A local disconnect relay LDR is providedto deenergize the answerdrawal of the calling plug from the associatedjack.

A ringing control relay RCR, a ringing interrupter relay RI and a partyline ringing key RK associated with the ringing generators G, G, G G andG provide means for signalling the desired subscriber on a local line. Acalling superviscry relay CSR and a calling supervisory lamp CS areprovided for the usual supervisory purposes. A flashing supervisorysignal control relay FCR connects the answering lamp AS to a constantlyrotating interrupter I to cause the lamp to flash to indicate a recallby a subscriber on a local to trunk connection. A listening key LKpermits the operator at the local exchange E to connect her set to thecord conductors so that she may properly time and supervise a local totrunk connection and answer a recall in response to the flashing recallsignal on such a connection. To the right of Fig. 1 I illustrate acalled local substation B associated with a line terminating at theexchange E in a line circuit L' consisting of line relay LR, cut offrelay CO, multiple line jacks J and multiple line signals S.

In Fig. 2 I show multiple trunk jacks TJ associated with multiple trunkbusy lamps TBL and a trunk cut ofi relay TCO which operates when thetrunk is busy to cause the illumination of the lamps TBL to inform theoperators before whom they appear that this particular trunk is busy.The apparatus just mentioned is all located at the local exchange E andthe dotted portion of the heavily marked conductors indicates the trunkline extending to a distant exchange F where it terminates in coils aand c of repeating coil RC.

-A condenser C is placed between the said coils a and 0 but a trunkbridging relay TAC is bridged across said condenser C and is actuated bycurrent from the connected cord circuit C to cause the operation of atrunk signalling relay TSI which lights the trunk answering lamp TAL toindicate an incoming call to the trunk operator. The trunk operators setTO can be connected thru the contacts of a trunk listening key 'ILK tocoils b and d of the repeating coil RC and condenser C connected inseries therewith.

A trunk sleeve relay TSL operates when the trunk plug TP is insertedinto a multiple jack J to interrupt the energizing circuit for the trunkansw g lamp TAL. A trunk. ringing key TRK and a ringing generator G areprovided to signal the subscriber T whose line terminates at theexchange F in a line circuit L consisting of multiple jacks J and lampsS line relay LR and a cut on" relay 00 LR is operated by current flowingfrom grounded battery thru relay LR, normal closed contact 2 of CO overthe line conductors and thru the closed contacts of the switchhook toground at normal contact 3 of CO. The relay LR energizes.

and closes its alternate contact 4 to complete an obvious operatingcircuit for the line signals S. The lamps S appear before a plurality ofoperators and any one of these operators can seize the incoming call tothe exclusion of the other operators. Assume that the operatorassociated with the cord circuit C seizes the call by inserting theanswering plug AP of the cord circuit C into the answering jack J of thecalling line. This insertion establishes an energizing circuit for theanswering sleeve relay ASL which circuit can be traced from groundedbattery thru windings 5 and 6 of ASL, conductor 7, normal closed contact8 of line disconnect relay LDR, sleeve contacts of the connected plug APand jack J, thru the winding of out off relay CO to ground. The sleeverelay ASL energizing closes its alternate contact 9 thereby shunting outits high resistance winding 6 and allowing the cut oil relay CO to beoperated by current flowing over the previously described path with theexception of high resistance winding 6.

The relay CO upon energization opens its normal contacts 2 and 3 whichinterrupts the energizing circuit of the line relay LR and causes itsrestoration to efface the line signals S by opening contact 4. The relayASL upon energizing closes its alternate contacts 10 and 11 to close thetalking conductors and to connect the operators set 0 to the talkingconductors over conductors 12 and 13, normal contacts 14 and 15 ofoperators disconnect relay ODR, conductors 16 and 1'7, alternatecontacts 10 and 11 of ASL, to tip and ring conductors of the cord 0. Theclosure of contacts 10 and 11 of ASL establishes a circuit for theanswering supervisory relay ASE which is operated for supervisorypurposes by current flowing from grounded battery thru the lower windingof ASR, alternate contact 11, thru the subscribers loop, alternatecontact 10, thru the upper winding of ASR to ground. If another operatorattempts to seize the call subsequent to the seizure by the operator ofthe cord C, the

'insertion of the answering plug of the second cord into a multipleanswering jack will have no effect upon the answering sleeve relay ofthe second cord as it cannot operate in shunt with the low resistancepath thru the winding 5 of ASL of cord C as the high resistance windingof relay ASL of the second cord is included in the circuit. The relayASL of the second cord does not operate and fails to connect theoperators set to the calling line and the operator failing to receive aresponse to her inquiry withdraws her plug from the jack. The relay ASRestablishes a circuit for the automatic answered call peg count meterwhich circuit may be traced from battery, normal contact 26 of CSL,conductor 59, normal contact of ODR, alternate contact 61 of ASR and themeter punching M which is connected to the metering apparatus (notshown) to register an answered call.

The operator of the cord C having been con-.

nected to the cord conductors as before described inquires the wants ofthe calling subscriber and learning that'a connection with thesubscriber B is desired tests the jack J' leading to the subscriber B bytouching the tip of the calling plug GP to the sleeve of the jack J. Ifthe line is busy 2. battery potential will be present on the v sleeve ofthe jack J.

This current will flow thru the tip conductor of CP, conductor 23,normal contact 24 of ODR, conductor 25, thru the tertiary winding of theoperators induction coil 010 to ground. This flow of current will causea click in the operator's head set and thereby indicate the busycondition of the called line. Upon the transmission of this informationto the subscriber A he replaces his receiver upon its switchhook and theoperator will disconnect the answering plug AP from the line jack J andrestore the circuits to normal.

If the called line is idle the operator inserts the calling plug CP intothe jack J of the called line thereby closing an energizing circuit forthe calling sleeve relay CSL and the cut-off relay C of the line circuitL. These relays are energized by current flowing from grounded batteryat the disconnect sleeve relay DSL, normal contact 17 of said relay,normal contact 18 of the trunk disconnect relay TDR, normal contact 19of the line disconnect relay LDR, conductors 20 and 21, the winding ofthe calling sleeve relay CSL', conductor 22, the winding of the .callingsleeve relay CSL, sleeve contacts of the connected plug CP and jack Jthrough the winding of the cut on relay CO to ground. The calling sleeverelay CSL energizes and closes its alternate contact 26 to establish anenergizing circuit for the operators disconnect relay ODR which isoperated by current flowing from grounded battery, alternate contact 26of CSL, conductor 27, winding of ODR to ground. The relay ODE opens itsnormal contacts at armatures l4, l5 and 24 to disconnect the conductors12, 13 and 25 which lead to the operators set from the cord conductors.

The closing of alternate contact 49 of relay ODE establishes anenergizing circuit for the flashing recall relay FOR which circuit canbe traced from grounded battery, alternate contact 49, conductor 50,alternate contact 51 of relay ASE, the winding of relay FOR/to ground.The opening of normal contacts 28 and 29 of relay CSL prevents theoperator from connecting her set 0 to the cord conductor should sheactuate her listening key LK. The closing of alternate contact 30 ofrelay CSL closes a circuit for the calling supervisory lamp CS tracedfrom battery, thru alternate contact 30, conductor 31, normal contact 32of calling supervisory relay CSR, normal contact 33 of CSL, conductor34, normally closed contact 35 of ringing control relay RCR, conductor36, the lamp CS to ground. The calling supervisory lamp CS is lightedover this circuit and remains in such condition until the operatordepresses the ringing key to signal the called subscriber at substationB.

The operator signals the subscriber at substation B by depressing one ofthe ringing key plungers of the party line ringing key RK to connectringing current of the proper frequency to operate the call signal atthe called substation B. Assuming that the generator G is of the properfrequency the key plunger associated with this generator is moved to itsfully depressed position in which position the end spring contacts 38and 39 of the ringing key RK are also closed. The closure of alternatecontact 38 of the end spring contacts establishes an energizing circuitfor the ringing interrupter relay RI which circuit may be traced fromground thru the winding of relay RI, conductor 37, alternate closedcontact 38, conductor 34, normally closed contact 33 of calling sleeverelay CSL', normally closed contact 32 of calling supervisory relay CSR,conductor 31, and alternate contact 30 of calling sleeve relay CSL togrounded battery. The relay RI energizes and closes its alternatecontact 42, thereby estabc lishing a circuit for the ringing current togive an initial ring at the called subscribers station. The circuit forthe ringing current can be traced from grounded side of the generator G,alternate contact 40 of key RK, conductor 41, alternate contact 42 ofrelay RI, alternate contact 29 of CSL, the tip contacts of connectedplug CP and jack J thru the call signal at the subscribers station B,the ring contacts of jack J and connecting plug CP, alternate contact 28of relay CSL, conductor 43, alternate contact 44 of ringing interrupterrelay RI to ground The ringing control relay RCR is also energized bycurrent flowing over the circuit closed at contact 39 of the end springswhich may be traced from ground thru the winding of ringing controlrelay RCR, conductor 40, alternate contact 39 of end springs, conductor34, normally closed contact 33 of CSL', normally closed contact 32 ofCSR, conductor 31 and alternate contact 30 of CSL to grounded battery toefiace the lamp CS and establish a locking circuit for itself whichcircuit can be traced from grounded battery, alternate contact 30 ofCSL, conductor 31, normally closed contacts 32 and 33, conductor 34,alternate contact 35, thru the winding of relay RCR to ground. Relay RCRcloses contact .46 thereby connecting a constantly rotating interrupterI in a series circuit with the ringing interrupter relay RI, thru thenormally closed contact 38 of the end springs of key RK, which assumedits normal position when released by the operator, which causes theintermittent operation of ringing interrupter relay RI to alternatelyconnect and disconnect ringing current to the called line. The breakingof normally closed contacts 62 and 63 by relay RCR opens the talkingconductors and prevents the flow of ringing current back to the calledsubscriber A. However, a revertive ringing tone is transmitted to thecalling subscriber to inform him that the operator is signalling thedesired party. This revertive ringing tone can be traced from thepunching RE which is connected to a ringing tone machine, not shown,alternate contact 64 of relay RI, to the heavily marked cord conductorwhich leads to the calling subscribers station A. The relay RIalternately opens and closes the make-before break contact 150 to form ashunt circuit across the called line to discharge any ringing currentwhich may be charged thereon and thereby prevent the operation of relayCSR by this charge to signal a false completion of the call.

The subscriber at the substation B in response to his call signalremoves his receiver from the switchhook and when the relay BI is in adeenergized position as it is during a silent period of the ringingcycle an energizing circuit is'established for the calling supervisoryrelay CSR. The relay CSR is operated by current flowing from groundedbattery thru the upper winding of relay CSR, conductor 46, normallyclosed contact 44 and relay RI, conductor 43, alternate contact 28 ofCSL, ring contacts of CP and J thru the closed switchhook contacts atsubstation B, the tip contacts of J and CP, alternate contact 29 of CSL,normal contact 42 of relay RI, thru the lower winding of relay CSR toground. The opening of normally closed contact 32 of CSR opens thelocking circuit of relay RCR which accordingly restores to normal todisconnect the interrupter I from the relay RI and prevent a furtheroperation of ringing interrupter relay RI. The opening of contact 32 ofCSR also breaks the operating circuit of the calling supervisory lamp OSto prevent its operation upon the closure of normal contact 35 of RCR.The calling subscriber at the substation A and the called subscriber atthe substation B are now in a conversational circuit which may be tracedover the heavily marked conductors and the interspersed condensers CDand CD.

Upon the termination of the conversation the subscribers at thesubstations A and B replace their receivers upon their respectiveswitchhooks. The replacing of the receiver at the substation A opens theenergizing circuit of the answering supervisory relay ASE at theswitchhook contacts and the relay ASE upon deenergization closes itsnormal contact 51, to establish an energizing circuit for the localdisconnect relay LDR which relay is energized by current flowing fromgrounded battery, alternate contact 49 of relay ODR, conductor 50,normal contact 51, alternate contact 52 of "PCB which is slow to releasedue to its construction, conductor 53, normally closed contact 54 ofCSL, conductor 55, normally closed contact 56 of TDR, thru winding ofLDR. to ground. Relay LDR operates and closes its alternate contact 58thereby establishing a circuit for the answering supervisory signal ASwhich can be traced from grounded battery thru the lamp AS, alternatecontact 58, to punching AP which is connected to ground thru a commonpilot relay, not shown in the drawings. A locking circuit for relay LDRis also established at contact 57 traced from grounded battery,alternate contact 49 of relay 0BR, conductor 50, alternate contact 57 ofrelay LDR thru winding of LDR to ground.

The replacing of the receiver at the called substation 33 opens theenergizing circuit of the calling supervisory relay CSR at theswitchhook contacts and the closing of its normal contact 32 againestablishes a circuit for the calling supervisory lamp CS thru alternatecontact 30, conductor 31, normal contacts 32 and 33, conductor 34 andnormal contact 35 of RCR. The restoration to normal of contact 48 of CSRinterrupts the energizing circuit of the calling sleeve relay CSL whichwas held'up thru alternate contact 48 after the local disconnect relayLDR. had operated to attract its armature 19. The restoration of contact30 of CSL interrupts the circuit for lamp CS but a substitute circuit isclosed at normal contact 28 of CSL. The lamp CS is maintained in itsoperated condition by current flowing from battery, normal contact 25 ofCSL, conductor 59, alternate contact of ODR, conductor 8'7, to ground atthe lamp CS. The disconnect sleeve relay DSL is operated by currentflowing from grounded battery thru the winding of DSL, conductor 21,resistance 65, sleeve contact of the plug CP and jack J to ground thruthe winding of the cut on? relay CO. The winding of disconnect sleeverelay DSL is of high resistance and its series connection with theresistance causes the cut off relay CO and relay CSL to release andthereby condition the called line for a line lamp recall or anotheroutgoing call.

The local disconnect relay LDR also attracts its normally closed contact8 to interrupt the circuit of the answering sleeve relay ASL whichrestores and opens the talking conductors at contacts 10 and 11. Theopening of contact 8 of LDR also causes the restoration of cut off relayCO so that the calling subscriber may initiate a recall by removing hisreceiver which will again bring about the energization of the line relayLR to light the line signals LS and the same operator who answered theoriginal call may seize the recall or any one of a plurality ofoperators may seize it as is well understood from the previousdescription.

AS and CSInow removes the plugs and C? from the respective jacks J and Jand the removal of the answering plug AP from the jack J disconnects theanswering end of the cord 0 from the calling line. The removal of thecalling plug CP from the jack J opens the energizing circuit of thedisconnect sleeve relay DSL which opens its contact 17 to cause therestoration of relay ODR.

The opening of contact 49 of ODR disrupts the energizing circuits of thelocal disconnect relay LDR and the answering supervisory lamp AS both ofwhich restore to normal. The restoration or" alternate contact 60 of ODReffaces the calling supervisory signal CS. The apparatus used inestablishing the connection above described is now at normal andavailable for establishing other connections.

If the called subscriber at B does not respond to his call signal thecalling subscriber at A can release the entire connection by replacinghis receiver upon its switchhook. The relay ASR deenergizes and closesits normal contact 51 to close an energizing circuit for the localdisconnect relay LDR which operates and interrupts the locking circuitof ASL and CO at contact 8 and closes an illuminating circuit foranswering supervisory lamp AS at contact 58. The deenergization ofrelays ASL and CO sever the calling line from the cord and enable thesubscriber at A to initiate a recall which will be evidenced by thelighting of the multiple line lamps S in the usual manner. The relay LDRinterrupts the circuit of CSL at its contact 19 which restores itsalternate contacts 26 and 30 to normal. The opening of alternate contact30 interrupts the locking circuit of ringing control relay RCR whichprevents the further application oi: ringing current to the called line.The calling supervisory lamp CS is illuminated by battery at normalcontact 26 of CSL to signal for a disconnection. The relay DSL operatesover a previously traced circuit to cause the deenergization oi the cutoiT relay CO which places the called line in its normal condition topermit the initiation of a new call in the usual manner. The operatorupon noticing the lamps AS and CS will withdraw the plugs AP and CP fromthe jacks of the lines with the results above described.

In the establishment of a local to trunk connection such as is necessarywhen subscriber A at exchange E desires to communicate with thesubscriber T at the exchange F the operation of the circuit arrangementshown in Fig. 1 is the same as previously described up to and includingthe connection of the operators set 0 to the cord conductors of the cordcircuit C. The operator inquires the wants of the calling subscriber atthe substation A and is informed that the subscriber at T is wanted. Theoperator inserts the calling plug CP into a multiple jack TJ of an idletrunk line terminating at her position and extending to the distantexchange F. This causes the operation of calling sleeve relays CSL andCSL and trunk out oii? relay TCO by current flowing from battery, normalcontact 17 of DSL, normal contact 18 of TDR, normal contact 19 of LDR,conductors 20 and 21, winding of CSL', conductor 22, Winding of CSL,sleeve contacts of CP and trunk jack TJ, winding of trunk cut off relayTCO to ground. Relay TOO closes its alternate contact 55 to establish anobvious energizing circuit for the multiple trunk lamps TBL which lightto inform the operators at the other posi- The operator noting the twolighted signals tions that this particular trunk is busy. The operationof sleeve relay CSL establishes an energizing circuit for the operatorsdisconnect relay ODR which is operated by current flowing from groundedbattery, alternate contact 26 of CSL, conductor 2'7, winding of ODR toground. ODR operates to disconnect the operators set 0 from the cordconductors. The operation of calling sleeve relay CSL' establishes acircuit for the calling supervisory signal CS which is accordinglyactuated by current flowing from grounded battery, alternate contact 30of CSL, conductor 31, normal contact 32 of CSR, alternate contact 33 ofCSL, conductor 87, lamp CS to ground. The calling lamp CS remainslighted until the subscriber at substation T answers the call.

The closure of contacts 28 and 29 of CSL establishes an energizingcircuit for trunk relay TAC the circuit for which can be traced fromgrounded battery, thru the lower winding of CSR, conductor 4'7, normalcontact 42 of RI, alternate contact 29 of CSL, tip contacts of CP andTJ, conductor 67, winding a of repeating coil RC, upper and lowerwindings of relay TAC, winding 0 of RC, conductor 63, ring contacts ofTJ and CP, alternate contact 28 of CSL, conductor 43, normal contact 44of RI, conductor 46, upper winding of CSR to battery. The relay CSR doesnot operate due to the high resistance of the windings of relay TAC. Theoperator throws her listening key LK to connect her operators set 0 tothe cord conductors thru alternate contacts '75 and '78 of CSL.

The bridging relay TAC is operated by the flow of current and closes itsalternate contact 69 to establish an energizing circuit for the trunksignalling relay TSI which is operated by current flowing from groundedbattery thru the winding of TSI, conductor '70, to ground at alternatecontact 69 of TAC. The relay TSI closes its alternate contact '71thereby establishing an energizing circuit for the trunk answering lampTAL which is operated by current flowing from grounded battery, thrulamp TAL, alternate contact '71 of TSI, normal contact '72 of trunksleeve relay TSL to ground. The lighting of lamp TAL informs theoperator attending the position at which the trunk line terminates thata call has been placed and she thereupon throws her listening key TLK toconnect her operators set TO to the talking conductors of the trunkcircuit which places her in a conversational circuit with the operatorat the exchange E. This circuit may be traced from the trunk operatorsset TO, alternate contact '73 of TLK, winding 13 of RC, condenser Cwinding (1, alternate contact '74 of TLK to the trunk operators set TO.

The other side of the circuit can be traced from operators set 0 at theexchange E, conductor 12, alternate contact '76 of LK, alternate contact'75 of CSL, normal contact 42 of RI, alternate contact 29 of CSL, tipcontacts or" the plug CP and trunk jack TJ, conductor 67, winding a ofRC, condenser C winding 0, conductor 68, ring contacts of trunk jack TJand plug CP, alternate contact 28 of CSL, conductor 43, normal contact44 of RI, conductor 46, alternate contact '78 of CSL, alternate contact'77 of LK, conductor 13, to operators set 0. The operator at O informsthe operator at T0 that the subscriber T is desired.

After testing the called line and finding it idle the trunk operatorinserts the trunk plug TP into the jack J associated with the calledline T. This causes the operation of trunk sleeve relay TSL and out 01frelay CEO by current flowing from grounded battery thru the winding ofTSL, sleeve contact of trunk plug TP and jack J the winding of cut offrelay CO to ground. The relay TSL operates and opens its normal contact'72 thereby elfacing the trunk answering lamp TAL. The operator nextactuates her trunk ringing key TRK to signal the called subscriber T.The circuit for the ringing current can be traced from the grounded sideof the generator G thru generator G alternate contact '79 of TRK, normalcontact 83 of TDA, tip contacts of plug TP and jack J 2 thru the callbell at the substation T, ring contacts of jack J 2 and trunk plug TP,normal contact '81 of TDA, alternate contact 30 of key TRK to ground.The subscriber T removes his receiver from its switchhook in response tothe call signal and as soon as the trunk ringing key TRK is restored tonormal the trunk supervisory relay TSR is operated by current flowingfrom battery thru the lower winding of TSR, winding d of RC, normalcontact of key TRK, thru the now closed switchhook contacts atsubstation T over the circuit previously traced for ringing current,back thru normal contact '79 of key TRK,

thru the upper winding of TSR to the other side of battery. The operatorrestores her listening kcyTLK to disconnect her operators set TO fromthe talking conductors of the trunk circuit. The closure of alternatecontact 84 of relay TSR provides an .energizing circuit for the callingsupervisory relay .CSR of the cord circuit C. This relay is operated bycurrent flowing from grounded batterythru the upper winding of CSR,conductor 46, normal contact 44 of RI, conductor 43, alternate contact28 of CSL, ring contacts of plug Cl and trunk jack TJ, winding 0 of RC,lower winding of relay TAC, conductor 85, alternate contact 84 of TSR,conductor 86, winding a of RC, conductor 67, tip contacts of trunk jackTJ and plug CP, alternate contact 29 of CSL, normal contact 42 of RI,lower winding of CSR to ground. Prior to the closure of alternatecontact 84 the relay TAC was held energized by the flow of current overthis circuit thru both windings of the relay TACw but the shunting ofthe upper winding of relay TAC by the closure of alternate contact 84 ofTSR provides a low resistance path for the flow or" current which allowsthe calling supervisory relay CSR to operate. CSR opens its normallyclosed contact 32 to efface the calling supervisory lamp CS whichinforms the operator that the subscribers are now in a conversationalcircuit.

Upon the termination of conversation the subscribers replace theirreceivers upon their respective switchhooks and the replacing of thereceiver at the called substation T at the distant exchange causes therestoration of the trunk supervisory relay TSR which restores itscontact 84 thereby opening the energizing circuit of the callingsupervisory relay CSR which closes its normal contact 32 to establish acircuit for the calling supervisory signal CS which circuit may betraced from grounded battery, alternate contact 30 of CSL, conductor 31,normal contact 32, alternate contact 33 of CSL', conductor 8'7, lamp CSto ground. The lighted lamp informs the operator that the trunksubscriber has restored his receiver to its switchhook.

The restoration of the receiver at substation A causes thedeenergization of answering supervisory relay ASR which restores itscontact 51 to its normal position to interrupt the energizing circuit ofthe flashing recall relay FCR. The relay FCR is provided with a coppersleeve to make it slow in releasing and the energizing circuit for thetrunk disconnect relay TDR is established and the relay TDR is operatedby current flowing from grounded battery, alternatecontact 49 or" ODE,conductor 50, normal contact 51, alternate contact 52 of FCR, conductor53, alternate contact 5% of CSL, conductor 88, thru the winding of trunkdisconnect relay TDR. The relay TDR closes alternate contact 89 to closea circuit for the lighting of answering supervisory relay AS whichcircuit can be traced from grounded battery thru the lamp AS, alternatecontact 89 of TDR, conductor 90, normal contact 91 of FCR to ground, notshown, on the answering pilot punching AP. The lighted lamp AS informsthe operator that the subscriber A has replaced his receiver.

The closure of alternate contact 92 of TDR provides a locking circuitfor itself which may be traced from battery, alternate contact 49 of0BR, conductor 93, normal contact 94 of listening key LK, conductors 95and 9S, alternate contact 92 of TDR, the winding of TDR to ground. Theopening of normal contact 18 of TDR opens the energizing circuit ofrelays CSL and CSL which restore to normal. The contacts 28 and 29 ofCSL restore to normal and interrupt the circuit for trunk relay TACwhich deenergizes and restores its contact 69 to cause the restorationof trunk signalling relay TSI which closes its normal contact 101 toform an operating circuit for trunk d sconnect relay TDA. Currentflowing from grounded battery thru the relay TDA, normal contact 101 ofT31, and alternate contact of TSL to ground operates relay TDA whichthereupon closes its alternate contact 102 to close a locking circuitfor itself and closes alternate contact 103 to light the trunkdisconnect lamp TDL. The lighting or" TDL informs the trunk operatorthat the subscribers are ready to be disconnected. The withdrawal of TPfrom J causes the deenergization of TSL which restores its contact 72 toopen the locking circuit of TDA which restores and eifaces the lamp TDL.It is evident from the above that the trunk is instantaneously releasedupon the replacement of the calling subscribers receiver. Therestoration of relays CSL and CSL allows the disconnect sleeve relay DSLto be operated by current flowing from grounded battery thru the windingof DSL, conductor 21,

resistance 65, sleeve contacts of plug CP andtrunk jack TJ, the windingof trunk cut off relay TCO to ground. The resistance of the winding ofrelay DSL is so high that the trunk cut off relay TCO will restore tonormal and open its contact 66 thereby efiacing the trunk busy lampsTBL. The relay DSL in operating establishes a substitute circuit thruits alternate contact 17 for the operators disconnect relay ODR, theoriginal. circuit for ODR having been broken at contact 26 of CSL whenthe said relay CSL restored. The restoration to normal of contact 26 ofCSL established a substitute circuit for the calling supervisory signalCS which circuit may be traced from grounded battery, normal con-' tact26 of CSL, conductor 59, alternate contact 60 of ODR, conductor 8'7 thruthe lamp CS to ground. The operator noting the display of both thedisconnect lamps removes the plugs AP and CP from their respectivejacks. The removal of the answering plug AP from the jack J causes thedeenergization of relay ASL and cut off relay CO. The removal of thecalling plug CP from the trunk jack TJ causes the deenergization ofrelay DSL and the relay ODR which restores its contact 60 to normal tointerrupt the energizing circuit of the lamp CS. The opening ofalternate contact 49 by the restoration of ODR breaks the lockingcircuit for the trunk disconnect relay TDR which restores its contact 89to normal to eiface the lamp AS. The apparatus used in establishing theconnection between the subscriber A and the trunk subscriber T is all atnormal.

Should the trunk circuit be seized by another cord before the trunk plugT? is removed from the jack J an operating circuit for relay TSI will becompleted as above described and T31 will close alternate contact 71 tolight lamp TAL. The circuit for TAL can be traced from grounded battery,lamp TAL, alternate contact 71 of TSI, alternate contact 175 of relayTSL which is still energized by reason of TP being in jack J andalternate contact 103 of TDA to ground. The trunk operator noting thelighted signal will answer the call in the usual manner.

If the called subscriber at T fails to answer the call signal thecalling subscriber at A replaces his receiver to give the operator adisconnect signal. The relay ASR restores to energize relay TDR whichattracts contact 89 to illuminate disconnect signal AS and opens thecontact 18 to cause the deenergization of relays CSL and CSL. Therestoration of contacts 28 and 29 of CSL cause the restoration of trunkrelays TAC and T81 and the subsequent energization of TDA and theillumination of trunk disconnect lamp TDL. The relay DSL operates andrestores trunk cut off relay TCO which efiaces the trunk busy lamps TBL.The lamp CS remains operated and as both lamps CS and A6 are lighted theoperator knows that the call been abandoned and removes the plugs AP andCP from the jacks.

If the calling subscriber wishes information relative to the trunkconnection as to the charges, wrong number, or any inquiry of a similarnature prior to the disconnection of the plugs AP and CP from therespective associated jacks, the removal of the receiver at thesubstation A causes the energization of the answering supervisory relayASR which attracts its armature 51 to close an energizing circuit forthe flashing recall relay FCR which circuit can be traced from groundedbattery thru the alternate contact 49 of ODR, conductor 50, alternatecontact 51 of ASR, the winding of PCB to ground. The relay FCR energizesand attracts its alternate contact 91 thereby establishing a circuit forthe answering lamp AS which is intermittently operated or flashed. Thiscircuit can be traced from grounded battery thru the lamp AS, alternatecontact 89 of TDR, alternate contact 91 of FOR, thru the constantlyrotating interrupter I, to ground. The operator at the cord C is theonly one that receives this flashing recall signal and she operates herlistening key LK to connect her operatcrs set 0 to the cord conductorsthru normal contacts 28 and 29 of CSL. The operation of the listeningkey LK breaks the locking circuit of the relay TDR at alternate contact94 of LK and the relay TDR and lamp AS restore to normal. If anotherparty is wanted by the calling subscriber A the operator will remove theplug 0? from the trunk jack TJ and insert the same into the jackassociated with the desired new party and proceed as previouslydescribed to complete the connection.

The operator upon noticing the flashing signal can also answer therecall by removing the calling plug CP from its connected jack insteadof throwing her listening key as above explained, The withdrawal of plugCP causes the deenergization of relay DSL which interrupts at contact 17the circuit for relay ODE which restores its contacts 14 and 15 toconnect the operators set 0 to the cord conductors. The opening ofcontact 49 restores the relay TDR which extinguishes the flashing signalAS by breaking the circuit therefor at contact 89 and the apparatus ofthe link circuit is ready to complete the new connection.

While I have shown and described a preferred embodiment of my invention,it is to be understood that changes and modifications will readilysuggest themselves to those skilled in the art, and I desire to belimited only by the scope of the appended claims. 7

Having described my invention, what I claim is new and desire to secureby United States Lctters Patent is:

1. A telephone system comprising local calling lines and called localand trunk lines, an operators link circuit having a pair of terminalsfor connecting said calling line to a called local line or a trunk line,means in said link circuit controlled by said calling local line on alocal to local connection for operatively disassociating said callingline from said link circuit, a supervisory signal in said link circuitlighted upon the operation or" said means, means in said link circuitfor rendering ineiiective the said first means when said local line isconnected to a trunk line, and subscriber controlled means foroperatively disassociating said link circuit from said trunk line.

2. A telephone system comprising local calling lines and called localtrun 1 s, an operators link circuit having a pair terminals forconnecting said calling line to a called local line or a trunk line,means in said link circuit controlled by said calling local line on alocal to local connection for operativeiy disassociating said callingline from the said link circuit, a supervisory signal in said linkcircuit lighted upon the operation of said means, means in said linkcircuit for rendering ineffective tie said first means on a local totrunk connection and for closing another circuit for said supervisorysignal to cause said signal to be intermittently operated, andsubscriber controlled means for operatively disassociating said linkcircuit from said trunk line.

3. A telephone system comprising local calling lines and called localand trunk lines, an operators link circuit havin a pair of connectingterminals for connecting said calling line to a called local line or atrunk line, a relay in said link circuit responsive to the connection ofa terminal of said link circuit to a called local line, means in saidlink circuit controlled by said calling line on a local to localconnection and said relay for disassociating said calling line from aterminal of said link circuit, said relay being ineffective when aterminal of said link circuit is connected with a trunk line to renderineifective the calling lines control of said means, and subscribercontrolled means operative upon a local to trunk connection todisassociate said link circuit from said trunk line.

4. A telephone system including a calling subscribers line, called localand trunk lines, a signal individual to said calling line, a linkcircuit for connectin said calling line to said called lines, a signalindividual to said link circuit, subscriber controlled means operativeon a recall for operating said first signal if said link circuit is usedto connect said calling line to a called local line, and for operatingthe second of said signals if said link circuit is connected to a calledtrunk line to denote a recall, and other subscriber controlled means foroperatively disassociating said link circuit from a trunk line on alocal to trunk connection.

5. A telephone system including a calling subcribers line, called linesof different character, an operators link circuit having a pair ofterminals for interconnecting said calling and called lines, anoperators telephone set, relay means in said link circuit for connectingsaid operators telephone set to said link circuit, other relay means fordisconnecting said telephone set from said link circuit, an operatorslistening key for connecting said telephone set and said link circuit,relay means in said link circuit responsive to the connection of aterminal of said link circuit to a called line of one character torender said listening key ineiiective to connect said operatorstelephone set and said link circuit, and subscriber controlled means foroperatively disassociating said link circuit from said called lines ofdiiferent character.

6. A telephone system comprising local calling lines and called locallines and trunk lines, an operators link circuit having a pair ofconnecting terminals for connecting said callin line to called lines, anoperators telephone set, relay means in said link circuit forautomatically connecting said operators telephone set to said linkcircuit, said means responsive to the connection of a connectingterminal of said link cicuit to said calling line, relay means in saidlink circuit responsive to the connection of a connecting terminal ofsaid link circuit to a called line for automatically disassociating saidoperators telephone set from said link circuit, means in said linkcircuit for connecting said operators telephone set to said link circuitsubsequently to the operation of said secondrelay means, said meansbeing rendered ineffective when said connecting terminal is connected toa called local line and subscriber controlled means for automaticallyoperatively disassociating said trunk line from said link circuit.

'7. A telephone system comprising local calling lines and called locallines and trunk lines, an operators link circuit having a pair ofterminals for connecting a calling local line to a called local line orto a trunk line, an operators telephone set, relay means in said linkcircuit for automatically connecting said operators telephone set tosaid link circuit, relay means in said link circuit for automaticallydisassociating said operators telephone set from said link circuit, anoperators listening key for connecting said operators set and said linkcircuit subsequently to the operation of said second relay means, meansin said link circuit responsive to the connection of a con nectingterminal to a called local line whereby the said listening key isrendered ineffective to connect said operators telephone set to saidlink circuit, and subscriber controlled means for operativelydisassociating said trunk line from said link circuit.

8. A telephone system comprising a calling line terminating at a localexchange, a called line terminating at a distant exchange, a cordcircuit and a trunk circuit cooperating to interconnect said lines,indicating means in said trunk circuit at said local exchange operableupon the connection of said cord circuit and said trunk circuit toindicate the busy condition of said trunk circuit, and subscribercontrolled means for releasing said indicating means.

9. A telephone system comprising a local calling line and a called line,an operators link circuit and a trunk circuit for interconnecting saidlines, means in said link circuit controlled over said lines foroperatively disassociating said trunk circuit from said link circuit,and means in said trunk for indicating the associated or disassociatedcondition of said circuits.

10. A telephone system comprising a calling line and a called line, atrunk circuit associated with said called line, an operators linkcircuit and a pair of terminals for interconnecting said called line andsaid trunk circuit, means in said link circuit for holding said trunkcircuit, and subscriber controlled means for rendering said holdingmeans ineifective.

11. A telephone system comprising a calling line and a called trunkline, an operators link circuit having a pair of terminals forinterconnecting said calling line and said trunk line, means in saidlink circuit for holding said trunk line, and means controlled over saidcalling line for rendering said holding means ineffective.

12. A telephone system comprising a calling line and a called trunkline, an operators link circuit having a pair of terminals forinterconnecting said calling line and said trunk line, means in saidlink circuit for holding said trunk line, and means controlled over saidcalling line prior to the completion of a trunk call for rendering saidmeans ineffective.

13. A telephone system comprising a calling line terminating at a localexchange, a called line terminating at a distant exchange, a trunk lineassociated with said called line and terminating in a jack at said localexchange, an operators link circuit having a pair of plugs one of saidplugs adapted to be inserted into said trunk jack to interconnect saidcalling line and said trunk line, and means controlled over said callingline for operatively disassociating said trunk line from said linkcircuit.

14. A telephone system comprising a calling line terminating at a localexchange, a called line terminating at a distant exchange, a trunk lineassociated with said called line and terminating in a jack at said localxchange, an operators cord circuit having a pair of plugs, one of saidplugs adapted to be inserted into said trunk jack to interconnect saidcalling line and said trunk line, and means controlled over said callingline for operatively disassociating said trunk line from said linkcircuit prior to the Withdrawal of said plug from said jack.

15. A telephone system comprising local calling lines, and called locallines and trunk lines, an operators link circuit having a pair ofconnection terminals for interconnecting said calling local and calledlocal or trunk lines, means in said link circuit controlled by saidcalling local line on a local to local connection for operativelydisassociating said calling line from a connection terminal of said linkcircuit, said means being rendered ineffective when said local line isconnected to a trunk line, and subscriber controlled means operable on alocal to trunk connection for operatively disassociating said trunk linefrom said link circuit.

16. A telephone system comprising local calling lines and called localand trunk lines, an operators link circuit having a pair of connec tionterminals for interconnecting said calling local and called local ortrunk lines, means in said link circuit controlled over said lines foroperatively disassociating said called lines from said link circuit.

17. A telephone system comprising a local calling line and a calledtrunk line, an operators link circuit having a pair of connectionterminals for interconnecting said lines, means in said link circuitcontrolled over said lines for operatively disassociating said trunkline from said link circuit.

BERT A. WALLACE.

